At variance, little is known on the coalescence of drops made of superfluids, for which viscosity is negligible.
Experiments on magnetically levitated helium droplets at 0.7 K temperature have been carried out some time ago by Maris
and coworkers.[1]}
Using a static magnetic field, drops of less than 1 cm radius were confined and made to collide at velocities as small as a few cm/s.
We have recently simulated this experiment using nanoscopic He droplets within the time-dependent density functional theory (TDDFT)
approach.[2]} The droplets were initially at rest and drawn together by the mutual Van der Waals (VdW) long-range attraction.
It was shown that the radius of the contact region grows as the root square of time after contact, similarly as
for low viscosity classical drops.[3]}, [4]}, [5]} This scaling has been also found for the
collision of self-bound quantum droplets made of ultradilute Bose mixtures of cold gases.[6]}
